Steam-expansion engine



Patented Aug. 3, 1926i.

airain 'VERNON BALFOUR HARLEY-MSON, OIE CIHEAM, AND REGINALD 50H31' FESIER, O??

' EPSOM, ENGLAND.

STEAM-EXFNSION ENGINE;

This invention relates to: steam or the like expansion engines and has reference particularly to steam engines where` steam engine, alsozopcrates under steam expandedv at the back of the combustion piston.

In such engines some of the steam is expanded under the edge of the piston skirt between it andthe base ofthe conforming cov r but the major portion is expanded behind the piston crown, between it and the extremity of the conf rming cover.. For the purposes of this specification this latter space will be referred. to as the steam cylinder.

Inl. engines of this type it isnecessary to provide a passage between the valve or valves and the steam cylinder for the admission and exhaust of thesteam to and from the cylinder, and it is found in practice that the cross sectional area of passage necessary for admitting steam to the cylinder is considerably smaller than that necessary for adequately exhausting it. This passage must therefore, be large enough for the latter purpose. In cases where it is necessary or desirable to place the valves outside the conforming cover, this passage must traverse the whole length of the piston skirt and as its whole volume acts as clearance volume, this clearance volume becomes normally large.

The object of the invention is to assure that the clearance volume due to this passage is reduced to the equivalent of a similar passage of suiiicient area for admitting steam.

lith this object in view the invention consists broadly of a steam expansion engine, in which steam is expanded on the underside Of the piston, comprising a cylinder cover which conforms both to the interior of the piston and to the exterior of the piston rod, which rod is so spaced from the surrounding part of the cover as to provide a passage for the steam and is so shaped that the cross sectional area of the passage increases during the stroke so as to 700,648, and in Great Britain March 26; 1923.

provide, towards the end of the stroke a cross sectional area suflicient to adequately exhaust the steam..

rlie invention may conveniently be carri-ed into effect .by'making the piston rod and the conforming. part lof the cylinder cover of; conical or. stepped form and providing between theman annular passage for the steam.

ln order that the invention may be clearly understood two embodiments of the same will now be described by way of example, by aid-of the accompanying somewhat diagrammatic drawingsinwhich Figure 1 is alongitudinal section through a conforming piston and7 cylinder cover according to one embodiment ofthe invention kshowing the piston atv the-commencement of its stroke.

position. of the piston relative to the conformingcover when the piston has com-` pletedi its outward stroke.

Figure 3 is asimilar view showing the position ofthe` pistonV when it has completed half its returnstroke.

Figures i and 5 correspond in all respects f to Figures 1 and 2 respectively excepting that the same illustratethe second embodiment of the invention wherein the piston rod is of conical form.

Corresponding parts will be referred to throughout the specification by like reference numerals.

In the drawings 10 represents the cylinder cover which projects up into the interior of the cylinder, not shown, and which also embodies the steam inlet and exhaust ports 11 and 12 respectively.

This cover is annular in form and comprises inner and outer Walls 13 and 14 respectively, the outer wall 111 conforming to the interior' of the piston 15 and the inner wall 13 conforming to the pistonrod 17. rllhe rod 17 and inner wall 18 are in the axamples illustrated in Figures 1, 2 and 3 of stepped form, and of such relative diameter as to provide an annular passage 18 between them, such passage functioning as an inlet passage for the steam on the outward stroke of the piston and an exhaust passage for the steam on the return stroke of the piston.

By reason of the stepped or conical form of the conforming parts of the piston rod and cover the cross sectional area of the passage 18 at the commencement of the stroke or the piston 1s suliclent ior tne proper admission ot the steam required, such cross sectional area increases however as the piston moves away from the cover so that when the piston commences its return or exhaust stroke the cross sectional area of this lpassage is at a maximum and7 in the examples illustrated in Figures l and 89 such maximum area is maintained through a distance indicated in the drawings, that "is until the piston reaches the position shown in Figure 3 after which the cross sectional area is reduced until the minimum is again reached when or before the piston reaches .the end of its return stroke. Such reduction in cross sectional area is however no detriment in practice as by the time the piston has reached the position shown in Figiire 3 most of the steam has passed out of the exhaust port. Further it is frequently desirable that a certain proportion of the steam 1oe trapped in the cylinder to provide the desired cushioning etlect of the end of the stroke and 'for this reason the exhaust valve will he shut or shutting when the piston is in the positionv sage 18 is reduced to the equivalent of a pas4 lof inletrareaV is possible due to short cut oit' andV hence low piston speed during admission. Y

lllhat we claim and desireto secure by Letters l atent-isz- Y y l. A steam expansion engine comprising a cylinder, a piston within said cylinder, a piston rod of diminishing diameter from its inner-end to its outer end, a cylinder cover conforming to both the interior of the piston and the exterior of the piston rod and a space between the interior of said cover and the exterior of said piston rod constituting a passage for admitting steam to the underside ot the piston which passage increases in cross sectional' areaduring the stroke.

2. A steam expansion engine comprising a cylinder, a piston within said cylinder, a piston rod of stepped form the largest diameter being at the end adjacent to the piston, cylinder cover conforming to both the interior or" the piston and the exterior of the piston rod and a space between the interior of said cover and the exterior of said piston rod` constituting a passage for admitting steam to the underside of the piston which passage increases in `cross sectional area during the stroke.

ln witness whereof We affix our signatures.

n VERNON BAliFOUR HARLEY-MASON. REGINALD JOHN FISHER. 

